Photosynthetic organisms are used as a general term of organisms that fix CO2 using light energy and particularly an alga indicates a kind of photosynthetic organism with high photosynthetic efficiency under excellent culture conditions. Since, the industrial cultivation of algae has been performed for more than half a century and there has been a demand for algae to be used as industrial raw materials, fuels, feed and raw materials of fine chemicals, and health food, it is considered that the algae production occupies an important place in the future of industry.
Since various useful carbon components are generated through the process of fixation of CO2, in the process of culturing algae, algae culture and the research on production of various carbon components through the culture have been actively conducted.
In the future, the need for early search for alternative fuels has been increased from the concern that fossil fuels are depleted and a demand for functional chemicals preferable for maintaining and improving health is increased due to an increase in health-oriented consumers. Therefore, there has been a growing interest in the useful components generated from algae.
In the related art, as an example of a method for producing a carbon component using algae, PTL 1 describes, as a production of ethanol useful for fuels or raw chemical materials, microalgae Chlamydomonas sp. MT-JE-SH-1 belonging to Chlamydomonas that produces ethanol from starch in cells by being grown at the salt concentration of seawater, accumulating starch in cells, and maintaining the cells under the dark and anaerobic atmosphere. As the means for solving the above-described problem, PTL 1 also describes a method for generating ethanol by culturing (1) microalgae Chlamydomonas sp. MT-JE-SH-1 belonging to Chlamydomonas that produces ethanol from starch in cells by being grown at the salt concentration of seawater, accumulating starch in cells, and maintaining the cells under the dark and anaerobic atmosphere and (2) microalgae Chlamydomonas sp. MT-JE-SH-1 belonging to Chlamydomonas at the salt concentration of seawater, accumulating starch in cells, and maintaining a slurry that contains the cultured alga body under the dark and anaerobic atmosphere while the pH thereof is maintained in the range of 6.0 to 9.0.
Further, as a method for producing an oil/fat component, PTL 2 describes a method for culturing a microorganism, that is, 4,7,10,13,16-docosapentaenoic acid-producing bacteria strain L59 (PERM P-18987) belonging to Labyrinthula in the Labyrinthulaceae, accumulating oils and fats containing 4,7,10,13,16-docosapentaenoic acid as a constituent fatty acid in bacterial cells, separating the bacterial cells, extracting the oils and fats from the separated bacterial cells using a solvent, and hydrolyzing the extract.
In NPL 1, the relation between generating oils and fats using marine algae and the salt concentration at the time of cultivation is examined and NPL 1 describes that the growth of algae is suppressed in a case where the initial concentration of the salt concentration exceeds 1.5 M and a high lipid content are generated in a case where the initial concentration thereof is in the range of 0.5 M to 1.0 M.